1. Field of the Invention
The invention concerns a device for pneumatically feeding powder from a container.
2. Description of the Prior Art
Such a device is known from the European patent document 0 184 994 B1. This device serves primarily to pneumatically feed powdery coating material which in a spray coating process is sprayed on articles to be coated. A device of this type makes it possible to withdraw the powder directly from bags, cartons, barrels, boxes etc. and automatically feed it directly to a spray device or spray coating system, without using a fluidizing container or other intermediate container. Before such devices were known the powder had to be transferred into a "fluidizing container" from the shipping containers in which it was delivered by the powder manufacturer to the powder user. Such "fluidizing container" comprises an intermediate bottom which is permeable to air. Through the intermediate bottom, upward from below, flows air in the form of many fine jets fluidizing the powder contained above the intermediate bottom, so that the powder particles "float or hover" in the air flow. This state is called "fluidized powder." This fluidized powder can be withdrawn pneumatically by a suction device and fed to the spray device of a spray coating system. The spray coating device may be a handheld gun or a mechanical gun installed in a spray coating system. The entire spray coating process, including the supply of the powder, can take place automatically. The device of the prior type and the device according to the invention fulfill both the two functions: they fluidize the powder and pneumatically feed it to a point of usage. In the prior device, a suction pipe and a compressed air feed line arranged parallel at a distance beside it extend through the lid of the container. Provided on the end of the compressed air line is an air distribution device featuring oblong air distributing elements from fine-pored material, through which elements the air discharges in the form of fine compressed air jets, fluidizing the powder on the bottom end of the suction pipe. Mounted on the upper end of the suction pipe, above the container lid, is a suction device that withdraws from the container fluidized powder and pneumatically feeds it to the point of usage in a feed air flow, for instance to a spray device of a spray coating system. The compressed air fluidizes the powder in the container not across the entire container cross section, but only in a small limited area below the suction pipe. During the powder withdrawal there is created below the bottom end of the suction tube a cavity into which powder slides continuously from the container. This sliding and thus the continuous filling of the cavity below the suction pipe, and thus also a continuous, uniform powder withdrawal, is improved by vibrating the container by means of a vibrator. Once the container is empty, the air distribution device must be removed from the bottom end of the suction pipe and from the bottom end of the compressed air feed line, the suction pipe and the compressed air line must be pulled out of the container lid, thereafter, both must be reinserted through the lid of a new, filled container, and the air distribution device must be fastened again on both. When different types of coating powder must be successively withdrawn from different containers for the coating of articles, the entire device must be extremely accurately cleaned at every change to a different container, since even the smallest powder residues in the device will adversely affect the coating quality. Upon prolonged operation, however, the device needs to be cleaned also if it has been used for a longer time only for one and the same powder type from different containers, so that no powder remainders will collect within it. Such powder accumulations would clog the flow paths, interfere with a uniform feed rate, and powder accumulations breaking loose would cause paint lumps and thus coating defects on the object being coated.
Known from the European patent document 0 008 270 B1, moreover, is a device for the pneumatic feeding of powder from a container, which device consists of two coaxial pipes of which the inner one is the suction pipe and the outer one a compressed air pipe. Their bottom ends form together an annular gap type nozzle which from the annular space between the two pipes directs compressed air in the form of a downwardly slanted ring-shaped compressed air jet at the cylindrical wall of the container. From the cylindrical container wall, the ring-shaped compressed air jet drives the powder down into the container center, at a slant, and from there into the bottom end of the suction pipe. Thus, unlike in the former device, the fluidization of the powder occurs not only across part of the container cross section but across the entire container cross section. To that end it is necessary for the powder container to have a relatively small, preferably circular cross section. According to the publication, the container of this prior device has a ball type shape and the bottleneck is provided with a threading and hangs on a support, into which the bottleneck is screwed. The tubular arrangement with the two pipes is installed in the support, airtight, coaxially with the container. The objective of this device is making it possible to empty the entire content of the container, without leaving powder remainders on the container wall.
Another device known from the European patent document 0 103 745 B1 as well serves to possibly completely empty the container. The tubular arrangement of the device is for that purpose directed not axially in the center of the container, but essentially diagonally through the container and into the corner of the container bottom. The container is set slanted allowing the powder to slide into this corner. Unlike the two aforementioned devices, this device does not employ compressed air but only a suction pipe. The air withdrawn from the container can be replenished from the surrounding atmosphere through a pipe which coaxially surrounds the suction pipe.
A finely powdered to granular material is to be understood as "powder."
The problem which the invention is intended to solve is to so develop the device of the initially cited European patent document 0 184 994 B1 that it can be slipped without disassembly, i.e., in ready-to-operate, completely mounted condition, through a guide opening providing guidance in the longitudinal direction of the pipe, of a container or other guide device, where the design at the same time should be such that the device features as few as possible spots on which powder may accumulate. At the same time, the device should be so designed that it will not be limited to the use of a specific container type or a certain slanted position or vertical position of a container. Furthermore, the design is to avoid the requirement of an additional support structure or container shape, as for instance in the said European patent document 0 008 270 B1, for the device or for the container. Instead, the device should be able to dip into the container solely by its deadweight, practically under gravity, while the device sucks powder from the container.
According to the invention, a device for pneumatically feeding powder from a powder container comprises a guide device that can be placed on the container and is supported by the container, a pipe arrangement installed axially in a guide opening of the guide device so that the pipe arrangement will penetrate deeper into the container as a powder quantity in the container decreases and, a vibrator vibrating the container. The pipe arrangement includes a suction pipe and a compressed air line having an upper end provided with a fitting for a compressed air supply and a bottom end upon which a nozzle head is provided from which many fine compressed air jets flow into the container, fluidizing the powder in a limited region of the container at a bottom end of the suction pipe. A feed pump is arranged at an upper end of the suction pipe and serves to suck the powder out of the container through the suction pipe. The pipe arrangement in completely assembled and ready-to-operate condition can be slipped from above the guide opening of the guide device into the container and can be completely pulled out of the guide opening without any need for disassembly or assembly of any parts. The compressed air line includes a pipe surrounding the suction pipe at a radial spacing defining an intermediate space. The suction pipe and the compressed air pipe are at their bottom ends mechanically connected with each other through a lower spacer and held spaced. This lower spacer is an element of the nozzle head. The upper ends of the suction pipe and the compressed air pipe are mechanically connected with each other through an upper spacer and kept spaced. The upper spacer is a fitting that supports the feed pump and connects the feed pump pneumatically with the suction pipe. The fitting additionally forms a connection from an external compressed air supply to the intermediate space in the compressed air pipe.
The invention offers the following advantages:
1. The withdrawal device can be slipped from above, through a guide opening of a guide device, specifically through a lid, and pulled out again without requiring the disassembly of parts of the device.
2. The withdrawal device soiled with powder and the lid, soiled with powder as well, need not be removed jointly from the container after it has been emptied, but it is possible to first remove the withdrawal device and then, separately, the lid from the container and clean it as well, which is considerably simpler than removing the lid together with the withdrawal device protruding through it, from the container.
3. The lid serves as a holder and axial guide of the withdrawal device, which is movable relative to the lid, through it.
4. The lid can be used for different containers, so that the powderfilled shipping containers do not need any specific lids of their own.
5. The withdrawal device may selectively be used with differently shaped and differently sized lids.
6. The withdrawal device is preferably arranged in the center of the container, coaxial with its center axis, but the withdrawal device may as well be arranged eccentrically or slanted to the container axis.
7. The suction withdrawal device requires no drive device for feeding it into the container while powder is sucked out, but the deadweight of the withdrawal device is inventionally balanced in such a way with the axially extending guide device of the lid that the withdrawal device will by its deadweight be lowered into the powder while powder is being sucked out. The powder container is preferably vibrated by a vibration device.
8. Several withdrawal devices extending through it may be arranged on the lid.
9. The lid may contain a sight hole for observation of the container content or may consist of transparent material.